Aaron Cheris, head of Bain's Americas retail practice, said the tight labor market is the single-biggest factor to watch this holiday season.

Across the entire supply chain, companies will be stretched thin as they try to limit out of stocks and speed up delivery times, Cheris said. That means they will be in a tough spot if shoppers insist on getting goods delivered or have a strict timeline.

"For the last-minute purchases that I really wanted to get before Christmas, am I going to bother if you tell me the delivery window is eight days and it's 3 days before Christmas?," he said. "They may say, 'Forget it. I'm not going to bother.'"